1.Field of the Invention
The present invention relates to determining link-level performance of random access channel (RACH) preamble detection in a communication system.
2.Description of Related Art
Expanded efforts are underway to support the evolution of the Universal Mobile Telecommunications System (UMTS) standard, which describes a network infrastructure implementing a next generation Wideband Code Division Multiple Access (W-CDMA) air interface technology. A UMTS typically includes a radio access network, referred to as a UMTS terrestrial radio access network (UTRAN). The UTRAN may interface with a variety of separate core networks (CN). The core networks in turn may communicate with other external networks (ISDN/PSDN, etc.) to pass information to and from a plurality of wireless users, or user equipments (UEs), that are served by radio network controllers (RNCs) and base transceiver stations (BTSs, also referred to as Node Bs), within the UTRAN, for example.
Setting up a communication channel typically involves the UE transmitting a known sequence, such as a sequence containing a series of symbols, on an access channel that is monitored by a receiver at the Node-B. The Node-B receiver detects the known sequence and uses it for functions such as estimating the round-trip delay between the UE and Node-B.
Methodology for characterizing system-level performance of this access channel, known in UMTS as a random access channel (RACH), is currently being investigated. System-level performance is typically represented by throughput and delay. Often, average link-level performance results, such as an average signal-to-interference ratio (SIR) versus detection probability, are used in a simulation of a network or system being evaluated. To generate link-level performance results, intensive link-level simulation is typically required, depending on Doppler and angle spreads.
FIG. 1 is a simplified block diagram of a conventional link-level preamble detection technique. Current determination of link-level performance of RACH preamble detection is characterized by a detection probability PD, given a false alarm probability (PFA). The detection probability represents a probability that a RACH preamble will be detected. The false alarm probability represents a probability of an erroneous detection of a RACH preamble when the RACH preamble is not actually present. A system or network simulation is arranged with specific channel parameters such as Doppler and angle spread. Intensive repeated system simulations are required, with detection results being collected over many repeated simulation runs.
Referring to FIG. 1, this current technique, illustrated as 100, involves performing a series of intensive simulations for a plurality of RACH realizations in order to determine a probability of detection of a given RACH preamble. For a given channel realization, such as a RACH realization, an instantaneous metric is determined (function 110) based on an input channel parameter such as transmit power, coefficients reflecting channel conditions, here shown as Ec/N0, which may represent a signal-to-noise ratio of a particularly received signal (e.g., a signal containing RACH preamble information), and parameters from spatial processing or temporal processing algorithms. This metric is used for determining a detection event (function 120). A threshold ‘q’ is also calculated for determining a detection event. This threshold is calculated (function 130) in advance based on a false alarm probability (PFA) requirement for the given channel realization. A comparison of the metric to q is performed in function 120 to determine a detection indicator value, IDet(q). The indicator value represents a detection success or a detection failure of the channel. If the metric is equal to or exceeds q, the value of IDet(q) is set to 1, otherwise it is set to zero (0).
Functions 110-130 are repeated for each simulation run evaluating a the performance of a particular channel realization, such as RACH preamble. After a simulation has been completed for all channel realizations of interest, a probability of detection (PD(q)) may be determined based on an average of the indicator values over all channel realizations (Function 140).
The above technique thus requires a series of simulation runs to determine a probability of RACH preamble detection. Moreover, the intensive link-level simulation described above captures only an average system behavior, rather than instantaneous system behavior. Accordingly, determining link level performance for a particular channel realization at a particular instant in time, so as to be able to simulate an instantaneous system behavior level, may be more advantageous to enhancing packet data and/or high speed data systems which arise in UMTS, W-CDMA and IEEE 802.11 technologies, for example.